The development of high-brightness LEDs has led to use of such devices in various applications and lighting fixtures. In general, an LED-based lamp operates in a fundamentally different way than an incandescent, or gas discharge lamp, and therefore may use a driver circuit tailored to deliver power to the LEDs according to their requirements. The driver circuitry for an LED-based lamp generally converts an alternating current (AC) input, such as a 120V/60 Hz line input to a stable direct current (DC) voltage used for driving the LED-based lamp. In some applications, for example automotive applications, the driver circuitry converts a DC input, such as from a 12V battery, to a stable DC voltage at a different level to drive the LED-based lamp.
The LEDs are often mounted on a thermal substrate, which in turn is electrically coupled to the driver circuit that may be located on a separate module. In addition to the mounting circuitry, the thermal substrate may include one or more thermistors used to monitor temperature and provide feedback to the driver for the purpose of limiting or regulating power, and thus temperature, to a desired operational range. In many applications, the connector between the driver module and the thermal substrate is of a pre-defined type or specification and the number of connector pins may be limited. In these cases it can be difficult to accommodate the extra electrical connections that would typically be needed to monitor a second thermistor.
One solution to this problem is to employ an additional, or intermediate, circuit board assembly on the thermal substrate to excite and monitor multiple thermistors and then transmit a composite signal back to the driver module over the single available electrical line to the driver module. This approach, however, suffers from the disadvantages of additional cost, complexity and size.